1. Field of the Invention
The present invention relates to a printing apparatus. More particularly, the invention relates to a printing apparatus which performs print registration upon bi-directional printing in which printing is performed during a forward scan and a reverse scan of a printing head or upon printing employing a plurality of printing heads.
2. Description of the Prior Art
Conventionally, printing registration of this kind is generally performed in the following manner.
For example, in the case of printing registration for the bi-directional printing where a forward scan and a reverse scan are performed to perform printing, a relative printing registration condition for the respective forward and reverse scans is varied by adjusting respective printing timing in the forward scan and the reverse scan and ruled lines are printed on a printing medium during the respective forward and reverse scans with use of the respective printing registration conditions. Then, a result of printing is observed by a user or the like to select the printing registration condition where best printing registration is achieved and a printing condition concerning the printing registration is set in a printing apparatus, a host computer or the like.
In the case of the printing registration between heads in the printing apparatus in which a plurality of printing heads are employed for printing, the ruled lines are printed by respective heads with varying the relative printing registration condition between the heads. Then, the printing registration condition where the best printing registration is attained is selected, by the user or the like, similarly to the above, to set the selected printing registration condition in the printing apparatus, the host computer or the like.
However, such conventional printing registration methods are accompanied by a troublesome operation that the user or the like observes a print result for the printing registration to select the printing registration condition and performs an operation for setting the printing registration condition. Therefor, some users, for whom such troublesome operation is unfavorable, may not perform the printing registration and use a printing apparatus in a condition containing a disagreement of printing positions between the respective forward and reverse scans or a disagreement of printing positions between the respective heads.
Furthermore, in the conventional methods, the printing registration condition can be selected only among respective printing registration conditions represented by printed patterns for the printing registration. For further printing registration with higher precision, it becomes necessary to perform printing of greater number of patterns with slightly varying the printing registration condition and it is also necessary for the user to distinguish delicate difference among the printed patterns to select the printing registration condition. In addition to trouble of the user, it takes a long period for performing the printing registration and require large number of patterns printed on the printing medium.
The object of the present invention is to provide a printing apparatus which can printing registration without troubling a user of the printing apparatus.
Another object of the present invention is to provide a printing apparatus which can perform an optimal printing registration irrespective of the ink to be used.
Still another object of the present invention is to provide a printing apparatus, wherein in the proximity of a scanning unit, there is provided an optical characteristic measuring unit for measuring optical characteristics of respective patterns which are printed during respective a first and a second printings to which printing registration performed, a plurality of density measurements are performed to the patterns by the optical characteristic measuring unit, and the print registration processing can be performed based on the measured density.
Still another object of the present invention is to provide a printing apparatus, wherein an interval between respective executions of pattern formation and measurement of the pattern can variously be adjusted so as to measure optical characteristics of the pattern by an optical characteristic measuring unit after a predetermined time elapses from the pattern formation during relative movement of a print head to a printing medium.
There is provided a printing apparatus for performing printing on a printing medium by using a print head, comprising:
scanning means for relatively moving the print head and the printing medium;
control means for controlling the print head to perform a first printing and a second printing which are a subject of printing registration so as to form a plurality of patterns, the plurality of patterns being formed in correspondence with a plurality of offset amounts in relative printing locations between the first printing and the second printing, respectively, and showing optical characteristics corresponding to the plurality of offset amounts, respectively;
optical characteristics measuring means provided on a location in the vicinity of the scanning means to measure the optical characteristics of each of the plurality of patterns formed by means of the print head controlled by the control means; and
printing registration means for performing printing registration processing of the first printing and the second printing based on respective the optical characteristics of a plurality of patterns measured by the optical characteristics measuring means.
It should be noted that throughout the description and claims the wording xe2x80x9cprintingxe2x80x9d means, in broad sense, not only forming significant information such as characters or graphics but also forming images, figures, patterns and the like on the printing medium or processing the medium irrespective of whether the information is significant or not and whether the information is overt or not in such a manner as to be visually perceived by a person.
Here, the wording xe2x80x9ca printing mediumxe2x80x9d means, in broad sense, not only paper to be typically used in the printing apparatus but also cloths, plastic films, metal plates and the like which can receive the ink.
Furthermore, the wording xe2x80x9cinkxe2x80x9d should be understood in broad sense similarly to the definition of xe2x80x9cprinting,xe2x80x9d and should include any liquid to be used for formation of images, figures, patterns and the like or for processing of the printing medium by applying the ink to the printing medium.
Throughout the description and claims, the optical characteristics include the optical density, namely, the reflection optical density using a reflection index and the transmission optical density using transmittance. But, an optical reflection index, the intensity of reflected light or the like may be used. In the following description and claims, the reflection optical density is mainly used as the optical characteristics and is simply referred to as the optical density or the density without any particular confusion.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof in conjunction with the accompanying drawings.